The IMMUNOLOGY AND MOLECULAR BIOLOGY CORE will provide the immunology and viral load assessments in support of the scientific agenda of this Program Project. For the biobehavioral intervention studies, Projects 0002 and 0004, viral load measurements of CD4 T cell counts will be made at baseline and just after a cognitive behavioral stress management (CBSM), as defined in the experimental design for these studies. Project 0002 studies gay and bisexual men; Project 0004 studies predominantly African- American women. For Project 0005 selected subjects from Projects 0002 and 0004 will undergo a laboratory reactivity study both pre-and post- intervention. The following immunology assays will be one on the serial samples collected on subjects; lymphocyte proliferation assays (LPA) in response to the mitogen phytohemagglutinin (PHA); antibodies to Epstein Barr virus (EBV), human herpes virus type 6 (HHV6) and herpes simplex virus type 2 (HSV2) natural killer cell cytotoxicity (NKCC) against the tumor cell target, K562; lymphocyte phenotypes using 4-color flow cytometry, determining number and percent of CD4, CD8 and subsets of these, using monoclonal antibodies specific for lineage, activation, differentiation and adhesion molecules. On these samples cytolytic potential of NK cells using anti-perforin antibody-based intracellular flow cytometry will be assessed and determination made of degree of expression of L-selectin (CD62L), LFA-1 (CD11a) and CD56 by fluorescence intensity measurements. Project 0005 will also include in vitro experiments to measure the effects of catecholamines and cytokines of NK activity, that will be done by this core.